A mass spectrometry method is a method for ionizing material particles (atoms or molecules) into ions, carrying out cytoplasmic-nuclear ratio separation on the ions by means of an appropriate stable or variable electric field or magnetic field in accordance with a spatial position, a time sequence and the like, and detecting the strengths thereof to perform qualitative and quantitative analysis. As the mass spectrometry method is used for directly measuring the material particles and has the characteristics of high sensitivity, high resolution, high flux and high applicability, a mass spectrometer and a mass spectrometry technology play an important role in modern science and technology. With the development of academic subjects such as life sciences, environmental sciences and medicine sciences, and on the basis of requirements for food security, national security and international counter terrorism, the mass spectrometer has become one of analysis instruments with highest demand growth rate. Particularly, as a chromatographic/mass-spectrometric combined technology appears, the technology is popular in all the fields or even indispensable due to a high separation function and high detection sensitivity on complex matrices.
A mass analyzer is a detectable component for separating ions in accordance with a cytoplasmic-nuclear ratio in the mass spectrometer, an ion trap is an important mass analyzer, and the principle of the ion trap is that a plurality of ions are stored in the trap and then separation detection is carried out. Compared with other mass analyzers excluding the ion trap, the mass analyzer including the ion trap can store the ions, and therefore MSn operations (mass spectrum operations such as MS/MS and MS/MS/MS) can be executed in the mass analyzer including the ion trap. The directions of the ion trap are defined as follows. An axial direction of a front end cover and a rear end cover of the ion trap is a Z direction, a vertical direction is an X direction, and a horizontal direction is a Y direction.
The MSn operations facilitate provision of structural information of the detected ions which can be called parent ions, and are very significant to accurate and qualitative analysis of the detected ions. The MSn operations can control identified ions and gas molecules (such as He and N2) to be fragmented due to collision, can also control the identified ions to be cracked due to photon absorption (such as infrared laser), and can also control the identified ions to react with electrons (such as an ECD mode) and anions (such as an ETD mode) to be cracked so as to generate sub-ions. The mass spectrometer further separates these sub-ions, and analyzes the strength of each sub-ion in a cytoplasmic-nuclear ratio (m/z, where m represents a mass number of ions and z represents a charged number of ions), thereby aiding in providing the structural information of the parent ions.
Not only a series of sub-ions of the parent ions are fragmented, but also a great number of neutral molecules which are not charged are fragmented. Due to the fact that these neutral molecules are not charged, the mass analyzer cannot operate the neutral molecules, and information thereof is often invisible, so that the neutral molecules are called lost neutral molecules.
It is very important to identify the structures of the fragmented neutral molecules of the parent ions for a great number of compounds, particularly biological molecules (protein molecules, polypeptide molecules, nucleic acid molecules and the like), and if the fragmented neutral molecules can be accurately, the structural information can be almost perfectly explained, which is a dream for the field of mass spectrometry.
Re-ionization of the fragmented neutral molecules of the parent ions is a possible solution. The neutral molecules in the mass analyzer can be re-ionized by ultraviolet light, and many mass spectrum experts make a lot of effort and tests, with little success.
Re-ionization of the neutral molecules in the mass analyzer by the ultraviolet light has some problems that:
there are very few neutral molecules generated by fragmenting the parent ions;
ultraviolet photons capable of entering the mass analyzer are not enough;
an opportunity (an ionized probability) of accepting the ultraviolet photons by the neutral molecules is not high; and
in a word, ions which are successfully ionized by the neutral molecules and the ultraviolet light are very few so as to hardly detect a signal. Moreover, the entire operation time sequence and logics are relatively complex, and it is hard to detect signals of a minority of ionized ions. In addition, the ionization time of the ultraviolet light is required to be accurately controlled, if the ion trap is irradiated by an ultraviolet lamp all the time, patent ions which are not fragmented are not ionized by the ultraviolet light and then cracked often, a mass spectrogram is unfavorably explained, and the difficulty in provision of the structural information is increased.